Abstract

Animation turns still drawings into motion by showing them rapidly in sequence. When images change fast enough, the human brain blends them together, creating the illusion of continuous movement. This process is the foundation of both traditional hand-drawn and modern digital animation. Devices like the Zoetrope in the 19th century demonstrated this principle long before cinema or computers.

In animation, each image is called a frame, and the frame rate—frames per second (fps)—controls how smooth the movement appears. Keyframes mark major positions in an action, while in-betweens (or “tweens”) fill the transition between them. Techniques like onion-skinning help animators keep drawings consistent across frames, and smear frames suggest fast motion by stretching shapes.

Animation students study timing, spacing, and the physics of movement to make drawings appear alive. Whether in 2D or 3D formats, the goal remains the same: to use sequential images to simulate motion that feels natural and expressive. Understanding these principles helps new animators plan actions, communicate emotion, and develop a professional workflow. This article introduces the fundamental terms and ideas behind movement in animation for high school students considering animation programs at university.

Keywords: animation, frame rate, keyframe, in-betweens, movement

Animation is built on a simple idea: still images, when shown one after another fast enough, appear to move. The human eye and brain merge these images into a single, fluid action. This illusion of motion is what makes cartoons, films, and digital games possible. Early devices such as the Zoetrope, a spinning cylinder with drawings inside, allowed people to see motion loops in the 1800s (Wikipedia, “Zoetrope”).

Each image in a sequence is called a frame. The frame rate, measured in frames per second (fps), defines how many images are shown each second. Standard film runs at 24 fps, while television often uses 30 fps. If the rate is too low, motion looks choppy. When the rate is high enough, the mind perceives continuous movement.

A keyframe marks a main point of motion—such as the top or bottom of a jump. Between keyframes are in-betweens, the drawings that fill the transitions. This process of adding intermediate drawings, known as “tweening,” creates smooth animation (Pixune, 2023). Modern software automates some of this, but the animator still defines timing and spacing, which determine the speed and weight of an action.

Students studying animation also learn to work “on ones” or “on twos.” Animating on ones means a new drawing appears in every frame; animating on twos means each drawing is shown for two frames. Working on twos saves time while still looking fluid at 24 fps. Fast actions or effects are often animated on ones for realism.

To maintain consistent motion, animators use a method called onion-skinning. It lets them see faint outlines of previous and next drawings, ensuring smooth transitions. For very rapid movements, they may draw a smear frame—one stretched or blurred image—to show speed without increasing frame count (Wikipedia, “Smear Frame”).

Animation students also study motion principles such as anticipation, squash and stretch, and overlapping action. These describe how objects start, continue, and end movement in a believable way. For example, a bouncing ball squashes when it hits the ground and stretches as it rises again. These effects convey weight and realism.

Although most professional animation today is digital, the same concepts apply as in hand-drawn methods. A 3D model still moves through keyframes and interpolation, just as drawn characters do. The illusion depends on timing, spacing, and the rate of frame change, not the medium.

Anyone exploring university animation programs can start learning these ideas with simple exercises. Flip-books, short digital loops, or frame-by-frame projects show how motion builds from small changes. By mastering keyframes, in-betweens, and timing, students begin to understand how static images gain life. Animation, at its core, is about observing how things move and translating that motion into drawings that convince the eye.